1. Field of the Invention
This invention relates to an ophthalmologic image processing apparatus for ascertaining the number of cells of a corneal endothelium in a photograph taken by projecting illumination light onto the cornea of a subject's eye.
2. Description of the Prior Art
In the medical field, it is said that the number of cells of a corneal endothelium ranges, as a whole, from 4,000 to 5,000 in infancy. When one of these many cells is died, the blighted cell is sucked by a cell adjacent to it. Accordingly, as we grow older, the number of the cells decreases and the corneal endothelium itself increases in size.
Further, it is said that a cornea may catch some disease, such as infection, due to no nutrition to the cornea if the number of the cells becomes below 500.
For this reason, if the number of the cells is below 500, a keratotomy is not usually performed from fear that the cells may be killed when the cornea is cut.
That is, in the field of ophthalmologic operations, an operator observes the state of the cells and counts the number of them before performing an operation on the cornea. In other words, the operator ordinarily ascertains whether a certain number of cells are still alive even if some cells are killed by the artificial cornea-cutting operation. After the operation, the operator inspects the state of the endothelium of the operated cornea at regular intervals of time.
As an apparatus for observing or photographing a corneal endothelium, a non-contact type of apparatus has been developed in which a slit lamp is provided with an optical attachment for observing a corneal endothelium.
In order to ascertain the number of the cells of the corneal endothelium, sample patterns A, B, and C which are hereinafter described are employed. For example, the sample patterns A, B, and C are each a square frame. FIGS. 4(A), 4(B), and 4(C) show the sample patterns A, B, and C, respectively. Hexagon-like cell patterns 10, 11, and 12 are represented on the sample patterns A, B, and C, respectively. The cell patterns 10, 11, and 12 are arranged to be different in size from each other because there is a correlation between the size of the cells and the number of the cells.
FIG. 4(C) corresponds to a corneal endothelium having large-sized cells the whole number of which is equal to, for example, 500. FIG. 4(B) corresponds to a corneal endothelium having medium-sized cells the whole number of which is equal to 1,000. FIG. 4(A) corresponds to a corneal endothelium having small-sized cells the whole number of which is equal to 1,500.
After photographing the corneal endothelium, the operator compares the size of the cells appearing in a photograph with the size of the cell patterns represented on the sample patterns, thereby judging that the photographed cells correspond to any of the cell patterns of the sample patterns A, B, and C, so that the operator ascertains the number of the cells.
For example, if the size of the photographed cells corresponds to the size of the cell pattern 11 represented on the sample pattern B, the operator presumes that the number of the cells is equal to 1,000. Likewise, if the size of the photographed cells corresponds to the medium between the size of the cell pattern 11 of the sample pattern B and the size of the cell pattern 12 of the sample pattern C, the operator presumes that the number of the cells is equal to about 750.
According to a method in which the size of the cells of the corneal endothelium is decided by using the sample patterns A, B, and C to ascertain the number of the cells, it is not required to employ a circuit for calculating the number of the cells or an expensive image analysis apparatus.
However, since an coincidence is not always brought about between the size of the photographed cells and the size of the cell patterns of the sample patterns, it is difficult to correctly count the total number of the cells of the corneal endothelium.